Make lavender simple syrup: Mix 1 cup sugar, 1 cup water, and dried lavender in a pot. Bring to a boil, then simmer for 5 minutes. Strain and cool.
Juice the lemons and strain out pulp and seeds.
Pour pineapple juice, lemon juice, water, and cooled lavender syrup into the pitcher. Stir well.
Chill the mixture for at least 2 hours.
Fill glasses with ice cubes. Pour the chilled mixture over ice.
Add pineapple wedges, lemon slices, and lavender sprigs as garnish.
Notes
Store leftover mocktail in the fridge for up to 3 days. The flavors blend better after 24 hours.For a stronger lavender taste, add more lavender syrup. Start with small amounts to avoid an overpowering flavor.To make ahead, mix all ingredients except garnishes and store in an airtight container.Use fresh pineapple juice for the best taste. Canned juice works too, but may be sweeter.